Project Summary In the USA, 5.6 million individuals with stroke face great difficulty performing activities of daily living, probably in part because they are unable to accurately judge the forces they generate with their two arms. The impact of this impairment on completing activities of daily living is unknown, but prior work suggests that the effect is substantial, particularly during bimanual tasks. I propose to examine the cause of the impairment, as well as to quantify its magnitude during unimanual and bimanual perceptual tasks. Furthermore, I propose to assess the plausibility of my novel hypothesis to explain the reason for force perceptual impairments by using a mechanistic probe. During the experimental testing, I will use custom mechatronic systems of my own design to control the user?s applied forces and to obtain quantitative outcome measures. Based on findings from this proposal, I will gain an improved understanding of the extent to which force perceptual impairments impact sensorimotor ability of individuals with stroke when executing unimanual and bimanual tasks. We know that after a hemiparetic stroke an individual?s paretic arm lacks the strength and control of their non-paretic arm. Therefore, these individuals with stroke must relearn to use their arms to interact with the world. For unimanual tasks, they normally relearn how to use each arm independently. For bimanual tasks, individuals with stroke nearly always learn to use their paretic arm to assist their non-paretic arm, not vice versa. Consequently, I propose the following novel central hypothesis: force perception is i) intact within each arm during unimanual tasks and ii) impaired only in the unusual condition when the non-paretic arm must assist the paretic arm to execute bimanual tasks. In turn, I propose that force perceptual impairments are important to investigate since they may hinder the ability of individuals with stroke to safely deal with unfamiliar and potentially dangerous bimanual tasks, such as when a knife slips while slicing a tomato. My proposed research and training plan benefits from its ability to unite engineers, neuroscientists, and clinicians to quantify changes in force perception following stroke. To test my central hypothesis, I will assess elbow force perceptual ability during unimanual and bimanual tasks, and I will test the neuroplasticity of force perceptual impairments by using bimanual training. Combined with my proposed automated, quantitative, mechatronic assessment tools, I provide a novel approach to mitigating maladaptive changes to perception following stroke and other brain injuries. Knowledge gained from this proposal can change the way clinicians approach rehabilitation by highlighting the importance of intact force perception during daily activities.